The present invention relates to electrical circuits and more particularly to direct current (DC) to direct current (DC) power conversion and regulation.
There is an ever increasing demand for power conversion and regulation circuitry to operate with increased efficiency and reduced power to accommodate the continuous reduction in size of electronic portable devices. Many times these devices are battery powered, and it is desirable to utilize as little power as possible to operate these devices, so that the battery life is extended. Therefore, the prior 5-volt industry standard has decreased to a 3.3 volt industry standard, which may soon be replaced by an even lower standard. Voltage regulators have been implemented as an efficient mechanism for providing a regulated output in power supplies. One such type of regulator is known as a switching regulator or switching power supply, which controls the flow of power to a load by controlling the on and off duty-cycle of one or more power switches coupled to the load. Many different classes of switching regulators exist today.
Due to the various industry power supply standards, a variable voltage DC/DC converter allows designers to program a desired supply voltage based on the standard being implemented. The variable voltage DC/DC converter gives the designer control of the output voltage by selecting values for certain external components, but also requires that the designer provide several compensation components to compensate for phase shifts in the output voltage that effect a desired negative feedback. For example, certain variable voltage DC/DC power supply devices require that the designer provide 6-12 external compensation components. The external compensation components are required so that the poles and zeroes associated with an amplifier device on the variable voltage DC/DC converter remain stable and do not move during normal operation. The conventional variable voltage DC/DC converter employs a single error amplifier that employs customer provided external compensation components configured to provide the required output voltage, poles and zeroes. The external compensation components require a large amount of real-estate to implement the desired DC/DC conversion.
FIG. 1 illustrates a conventional variable DC/DC converter system 10 comprised of an integrated control circuit 12 and customer supplied components that provide both the feedback voltage and the compensation for the variable DC/DC converter system 10. The integrated control circuit 12 includes an input feedback pin (P1), an output feedback pin (P2), and an output voltage pin (P3). The input feedback pin (P1) is coupled to a negative terminal of an amplifier device 14. The amplifier device 14 compares a voltage at input feedback pin (P1) with a reference voltage VREF. The output of the amplifier device 14 is provided at the output feedback pin (P2), and as input to a pulse width modulator 16. The pulse width modulator 16 provides a switching signal to a driver 18 coupled to the output voltage pin (P3). The output of the amplifier device 14 controls the duty cycle of the switching signal provided by the pulse width modulator 16. A customer supplied coil L is coupled to the output voltage pin (P3) and a charge capacitor C.
Energy builds up in the inductor L when voltage is applied to the inductor L, which is transferred to charge the capacitor C to an output voltage VOUT. A supply voltage VSUPPLY is provided at the inductor L through the driver 18 controlled by the pulse width modulator 16. The output voltage VOUT on the capacitor C is a function of the duty cycle of the pulse width modulator 16. The output voltage VOUT is fed back to the input feedback pin (P1) of the control circuit 12 through a first impedance component 22. The control circuit 12 utilizes the feedback signal to continuously adjust the duty cycle of the switching signal driving the inductor L, and as a result, providing the regulated output voltage VOUT. The output voltage VOUT is a function of a voltage divider formed by the first impedance component Z1 and a resistor R, and the reference voltage VREF.
The gain of the amplifier 14 is a function of a second impedance component 20 and the first impedance component 22. The first impedance component 22 and the second impedance component 20 are each comprised from about 3 to about 6 different components. The components of the first impedance component 22 and the second impedance component 20 control the gain, control the constants and control the output voltage of the conventional variable DC/DC converter system 10. The components of the first impedance component 22 and the second impedance component 22 include compensation components. The compensation components are provided to maintain a phase shift under 180xc2x0, caused by the inductor L and capacitor C combination (L-C filter), so that the feedback remains negative.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention relates to a variable voltage DC/DC converter system that separates the feedback voltage function and the compensation function of the DC/DC converter system into two different devices. A compensation device and compensation components can then be integrated into a single integrated circuit. A feedback voltage device is integrated into the single integrated circuit. The output voltage of the DC/DC converter is fed back to a voltage divider circuit. The voltage divider circuit includes a first resistor and a second resistor. The values of the first resistor and the second resistor determine the output voltage of the DC/DC converter system. The first and second resistors can be external to the integrated circuit and selectable by a customer. Alternatively, the first resistor is integrated into the integrated circuit, while the second resistor is external to the integrated circuit and selectable by the customer. The feedback voltage device receives the feedback signal through the voltage divider and provides the feedback signal to the compensation device. The compensation device then provides a duty cycle control signal that controls the duty cycle of a pulse width modulator. The pulse width modulator switches a supply voltage xe2x80x9cONxe2x80x9d and xe2x80x9cOFFxe2x80x9d to an output pin. A customer supplied inductor and capacitor combination provide the desired output voltage based on the duty cycle of the pulse width modulator based on the selected resistor values.
In one aspect of the invention, the compensation function of the DC/DC converter system is comprised of an amplifier device, a first impedance component coupled to the input of the amplifier device, and a second impedance component coupled between the input and output of the amplifier device. The first and second impedance components include a plurality of compensation components that compensate for an output voltage phase shift to maintain a phase shift under 180xc2x0, so that the feedback signal remains negative. The feedback device is comprises of a wide band amplifier device that includes a third resistor coupled between an input and an output of the wide band amplifier device. The first and second resistors determine the output voltage of the system, while the first and third resistors determine the gain of the system to mitigate amplifier offset. The present invention also includes methods for fabricating a variable DC/DC converter system and a method for operating a DC/DC converter system in accordance with different aspects of the present invention.